Exhaust nozzle



March-20, 1945. P. J.ICAYMPBEL'L I I 2,372,053

EXHAUST NOZZLE .Fil edSept. 27; 1941 INVENTOR Paul JCampbeil a ar/2 4;9. M

ATTORNEY tion of a still further Patented Mar. 20, 1 9145 EXHAUST Nozzu:

Paul J. Campbell, South Glastonbury, Conn., as-

signor to United Aircraft Corporation,v East Hartford, Conn., acorporation of Delaware Application September 27,

1941, Serial No. 412,674

,4 Claims. (Cl. .6035.6)

' This invention relates to improvements in fluid jet producing nozzlesand has particular reference to an improved nozzle for directing theexhaust gases of an internal-combustion engine into a reaction jet.engine crankshaft, not illustrated, in a manner An object of theinvention resides in the provision of an improved fluid nozzle of thecharacter indicated arranged to produce reaction jets of maximumeificiency when the pressure differential between the gas within thenozzle and lo the air at the nozzle exit is both aboveand below thecritical value.

A further object resides in the provision of an improved fluid jetdirecting nozzle of the character indicated which acts as a convergentl3 nozzle under some circumstances and as a convergent-divergent nozzleunder different circumstances.

Other objects and advantages will be more particularly pointed outhereinafter or will be- '2 come apparent as the description proceeds.

In the accompanying drawing, in which like reference numerals are usedto designate similar parts throughout, there is illustrated in severalslightly modified forms a suitable mechanical embodiment for the purposeof disclosing the invention. The drawing, however, is for the purpose ofillustration only and is not to be taken as limiting or restricting theinvention since it will be apparent to those skilled in the art thatvarious changes in the illustrated'embodiment may be resorted to withoutin any way exceeding the scope of the invention.

In the drawing,

Fig. 1 is a somewhat diagrammatic sectional viewer a fragmentary portionof an engine cylinder'with an exhaust gas Jet directing :nozzleconstructed according to the invention applied thereto.

Fig. 2 is an end elevational view of the nozzle shown in section in Fig.1.

- Fig. 3 is a longitudinal sectional view of the exit end portion of asomewhat modified form of fluid jet directing nozzle. r g

Fig. 4 is an end elevational view of the'nozzle shown in Fig. 3.

Fig. 5. is a sectional view oi the exit end por-' modified form ofnozzle.

Fig. 6 is an end elevational view of the nozzle r illustrated in Fig. 5.v

Fig. '7 is a longitudinal sectional viewoi a still further modified formor nozzle, and

Fig. 8 is an end elevational view of the nozzle illustrated in Fig. 7.

Referring to the drawing in detail, and parpulsive effort of the engine.In

' may, however,. be

ticularly to Figs. 1 and 2, the numeral Ill indicates aninternal-combustion engine cylinder within which there is a reciprocablepiston l2 connected by a suitable connecting rod H to the well known tothe art. The engine may have a plurality of cylinders all of the samegeneral form and construction and each cylinder maybe connected with anexhaust gas jet directing nozzle constructed according to the invention.

The cylinder 10 is also provided with an intake valve, not illustrated,'and an exhaust valve l6 controlling the opening of an exhaust gas portl8 in the closed end of the cylinder. The intake and exhaust valves maybe operated by suitable valve gear mechanisms, not illustrated in theaccompanying drawing but of some suitable form known to the art.

When the exhaust gases are ejected from the cylinders of aninternal-combustion engine these gases retain a considerable amount ofenergy which the engine has been unable to absorb and transmit intomechanical power. This energy is in the form of pressure, velocities,and heat energy and the complete waste of this residual exhaust gasenergy has previously been con-. sidered a necessary condition to theoperation of internal-combustion engines. Recent experiments, with highspeed aircraft have indicated that a; portion 01' this residual exhaustgas energy may be recovered bydirecting the exhaust gases rearwardly ina high speed Jet adding the reactive thrust of the exhaust gas Jets tothe proorder to obtain this, conversion of exhaust gas energy theexhaust gases are led through a rearwardly directed conduit whichterminates in a convergent restricted nozzle which emits. the exhaustgases at highvelocity in a rearward direction. Such previousinstallations have utilized a separate nozzle for each engine cylinderand have also utilized compound nozzles through which the exhaust gasesfrom several ylinders are ejected, and some have gone so far as .toelect all of the, exh'a'ust gas from an engine through a single nozzleconnected with the engine cylinders by means of a suitable exhaustconduit. For various reasons, such as lightness and maximum efliciency,the arrangement in which a separate nozzle is provided for each enginecylinder is thought to be superior and it is among the objects of thisinvention to provide an-improved nozzle form for such an arrangement.The improved nozzle used'with an exhaust manifold or collectorring incases where it is not desired to provide a separate nozzle for eachcylinder.

The pressure of the exhaust gas leaving the engine cylinder variesgreatly over the time of the exhaust stroke, particularly in modernengines in which the exhaust valves may be left open for as much as twohundred and sixty degrees of crankshaft revolution. At the beginning ofthe exhaust condition in which the exit endof the nozzlerepresents anaperture, the pressure within the nozzle represents the fluid pressureat one side of the aperture and the pressure of the air at the nozzleexit represents the fluid pressure at the opposite side of the aperture.According to wellknown physical principles a gas flowing from a regionof high pressure to a region of lower pressure through a convergentpassage will expand with decreasing pressure and increasing velocity.The final pressure to which it can expand within the convergent passagedepends on the ratio of pressures in the regions ahead of and after thethe nozzle and thegoutside atmosphere does not exceed the critical ratioof approximately two to one, and which will act as convergent-divergentnozzle when the pressure of the exhaust gases nozzle. When the pressureahead of the nozzle v is less than approximately twice the pressureafter the nozzle, the gas will expand to a pressure equal to that of theregion into which it discharges; However, if the pressure ahead of thenozzle is greater than approximately twice the pressure after thenozzle, the gas will expand within the nozzle only until it reaches a.pressure equal to approximately half the initial pressure.- It will,therefore, issue from the nozzle at a pressure above that of thesurrounding atmosphere. Since the velocity is determined by theexpansion ratio, the velocity of discharge from a convergent passage islimited to the velocity obtained by expansion through a pressure ratioof approximately two to'one. It is known that to expand a gas throughpressure ratios of more than two to one, it is necessary to add adivergent exit to the convergent passage. The gas can thus be expandedto a pressure equal to that of the surrounding, atmosphere, and thedischarge velocity is then determined by the ratio of initial to finalpressures rather than the critical ratio of two to one.

In the case of a nozzle attached to the exhaust port of an aircraftengine, the ratio of pressures before and after the nozzle fluctuatesrapidly from very high values to less than two to one. In order toexpand the exhaust gas completely to atmospheric pressure for allvaluesof this flu-ctuating pressure ratio, it is necessary to provide a nozzlewhich will operate eiiiciently under various pressure ratios above andbelow the critical value of approximately two to one. From the precedingdiscussion, it will be seen that a convergent passage is sufficient forexpansion through pressure ratios of less than two to one, but that adivergent exit is required for greater pressure ratios.

With theseconsiderations in view. it is among the objects of thisinvention to .provide an improved exhaust gas directing nozzle whichwill act as a convergent nozzle or orifice as long as the pressuredifferential between the exhaust gas in is more than twice as great asthe pressure of the air at the nozzle exit.

In accomplishing this object the nozzle, generally indicated at 20, isprovided at its exit end with one'or more inner partition members, suchas the members shown in Figs. 1 and 2 and indicated by the numeral 22.The nozzle 20 has side walls which converge to a location of minimumcross sectional area illustrated in the drawing as a neck 24. This neck24 constitutes an exit or aperture for the convergent channel ahead ofit and beyond this aperture the nozzle is somewhat expanded to providean enlarged end portion-26. The inner member 22 is uniformly spaced fromthe inner surface of the end portion 26 and has an internalcross-sectional area substantially the same as the cross-sectional areaof the neck or throat portion 24. The inner end of the member 22terminates somewhat short of the neck 24 in order to provide anadditional gas passage from the neck between this inner member and theenlarged end portion 26, and the inner end of the member 22 ispreferably somewhat rounded to provide a smooth entrance for exhaust gasflowing through this member from the neck portion 24.

With this arrangement, when the pressure differential of the gas withinthe nozzle 20 and the outside atmosphere is below the critical value thegas will flow from the neck directly through the inner member 22 and thenozzle will act as a straight or simple convergent nozzle but, when thispressure differential exceeds the critical value, a portion of the gaswill be forced to new through the space between the inner member 22 andthe enlarged end portion of the nozzle. As the cross-sectional area ofthis space plus the cross-sectional area of the inner member 22 isgreater-than the cross-sectional area of the neck portion 24 the nozzlethen becomes a divergent nozzle. and increases the jet velocity as thepressure differential between the gas within the nozzle and the outsideatmosphere increases up to the expansion capacity of the nozzle. Thisnozzle will, therefore, act both as a simple convergent nozzle and as aconvergent-divergent nozzle depending upon the value of the pressuredifierential between the gas within the nozzle and the outsideatmosphere.

In the form of the invention shown in Figs. 3 and 4 the principlesinvolved are the same as those explained above but the expansioncapacity of the nozzle has been increased by incorporating" therein anadditional inner member 28 disposed between the inner member 22' and theenlarged end portion 26 extending beyond the neck 24' of. the mainnozzle 20'. This intermediate member 28 is provided with a straightentrance portion 30 and an enlarged divergent portion 32 sur roundingthe inner member 22' and uniformly spaced therefrom as well as from theinterior of the enlarged end portion 26'. With this arrangement, whenthe above mentioned pressure differential is below the critical valuethe gas will flow through the neck v2t of the main nozzle, through thestraight portion 30 of the intermediate member 28 and through thestraight inner ,member 22' to the atmosphere and the nozzle will thenact as a simple convergent nozzle. When the pressure differential isslightly above the critical value. the gas may flow from the neckportion 24 of the main nozzle through the straight portion 30 of theintermediate member 28 and from thence through the inner member 22 andthrough the space between the inner member and the expansion portion 32of the intermediate member 28 thus providing a modifiedconvergent-divergent nozzle and, when the pressure difierential ismaterially above the critical value the gas may flow through the spacebetween the intermediate member 28 and the enlarged end portion 26',inaddition to the space between the members 22 and 28 and through themember 22 thus providing a further divergent effect to take advantage ofthe increased pressure differential.

In the form shown in Figs. 5 and 6 the principles are the same as thosedescribed for Figs. 1 and'2 and the only material difierence is that theenlarged end portion 26b of the main nozzle 20 is flared outwardlytowards the open end of the nozzle thus giving an increased expansioneffect to the space between this enlarged end portion and the innermember 22.

The form shown inFigs. 7 and 8 is the same as that shown in Figs. 1 and2 except that the nozzle is given a somewhat difl'erent form beingrelatively straight instead of curved as shown in Figs. 1 and 2, andhaving a circular cross-section rather than the substantiallyrectangular crosssection shown in Figs. 1 and 2. In this last form ofthe invention the nozzle is generally indicated at 34 and has a somewhatelongated neck-portion 35 leading into the enlarged end portion 38within which is located the circular inner member 40. The principles ofoperation of this modified form of nozzle are, however, in all respectssimilar to the principles described above in connection with Figs. 1 and2'. I

While a suitable mechanical embodiment has been hereinabove describedand illustrated in the accompanying drawing, in several slightlydifferent forms, for the purpose of disclosing the invention, it is tobe understood that the'invention is not limited to the particularembodiments so illustrated and described but that such changes in thesize, shape and arrangement of the various parts may be resorted to ascome withinthe scope of the sub-joined claims.

Having now described the invention so that others skilled in the art mayclearly understand the same, what it is desired to secure by LettersPatent is as follows:

1. A fluid ejection nozzle comprising, a convergent portion having arestricted neck, an enlarged end portion beyond said neck portion in thedirection of fluid flow, and a tubular member of substantially the samecross-sectional area as said neck within said enlarged portion, andradially spaced therefrom, said member also being axially spaced fromsaid neck in thedirection of fluid flow whereby fluid may flow from saidn'eck portion through said tubular member or through both said tubularmember and the space between said tubular member and said enlarged endportion.

2. -A nozzle for directing engine exhaust gases into a rearwardlydirected high velocity jet comprising, a convergent nozzle portion forreceiving the exhaust gas from the engine, a divergent nozzle portionconnected to the convergent nozzle portion for expanding said exhaustgas, and is cylindrical tubular member within said divergent portion andspaced radially from saiddivergent portion and axially from saidconvergent portion.

3. A nozzle comprising, a convergent nozzle portion for receiving gas, adivergent nozzle portion connected to the convergent nozzle. portion forexpanding said gas, and a member within said divergent portion andspaced therefrom to form an exit passage therebetween, said memberhaving a non-divergent exit channel therein.

4. A nozzle as set forth least one auxiliary member which increasesuniformly in cross-sectional area in the direction of fluid flow locatedbetween said non-divergent channel member and said divergent portion.

PAUL J. CAMPBELL.

in claim 3 including at

